Review your call history
Locate your call history in the center of the calls experience. There you'll see a list of past calls, including missed calls.
Go to Calls 
> History. From any call in the list, select More actions 
> Call back to begin a call automatically.
You can also chat with that contact, add them to speed dial, and add them to your contacts — all from the More actions menu.
Access your voicemail
Your voicemail is a familiar tool for getting the most out of your calling experience in Teams. To access your voicemail, go to Calls > History and then select Voicemail.
Call someone back by hovering over a voicemail and selecting Call or by selecting More actions 
and choosing Call back .
When you select a voicemail, you can review and access details and other information—all on the right side of Teams.
From here, you can:
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Listen to your voicemails by using the playback controls at the bottom.
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Review your voicemail summaries and transcripts (if available).
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Call someone back by using the call controls under the contact details at the top.
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Customize voicemail settings (such as recording a greeting and specifying call answering rules).